1. Field of the Invention
This invention relates to improvements in a vapor recovery system for a fuel filling installation which, by achieving more effective and quicker recondensation of the indrawn vapor both in the underground tank and in the vent pipe, and substantial decreasing-density separation of the air-vapor mixture within said vent pipe, allows effective and complete recovery of all the vapor present in the motor vehicle tank to be filled, without danger of explosion or undesirable pressurization of the underground tank and without using further vapor recondensation or separation units.
2. Description of the Related Art including information disclosed under 37 C.F.R. .sctn..sctn.1.97-1.99.
More specifically, the present invention relates to improvements in the vapor recovery system of the preceding U.S. Pat. No. 5,038,838 granted Aug. 13, 1991 to Giorgio Bergamini and Ernesto Paris for "System For Safe Vapour Recovery, Particularly Suitable For Fuel Filling Installations".
In said applications, vapor recovery is achieved by using a delivery gun without members for sealing against the filler pipe of the vehicle tank to be filled, together with controlled draw-in of the arising vapor-air mixture by a variable speed positive displacement pump, the speed of which is continuously adjusted in accordance with the volumetric flow rate of the delivered fuel, such as to draw a volumetric quantity of the air-vapor mixture equal to the volumetric quantity of fuel delivered plus a possible air excess depending on the temperature of the underground tank and the vehicle tank to be filled, and of which the discharge pipe extends to the bottom of the underground tank so that the bubbling of the air-vapor mixture through the fuel in said tank results in the mixture temperature and hence its volume being rapidly adjusted to the temperature of the tank itself. In addition a costly recondensation unit is used for the excess vapor within the dome of the underground tank, this excess arising when the recovered vapor is at a lower temperature than the underground tank, this happening for example during winter periods.
This known arrangement allows effective open-system recovery of the air-vapor mixture as it continuously adapts the mixture flow rate to the volumetric flow rate of the delivered fuel and to the temperatures of said tanks. It is however not able to recover the excess vapor created in the vehicle tank by a certain "champagne" effect, which has never been taken into consideration in current recovery systems, and which is determined by the inevitable violent impact of the delivered fuel against the walls of the filler pipe and tank, and by its mixing with the residual fuel contained in the tank, this giving rise to numerous minute bubbles or foam, which by increasing the heat transfer area results in increased evaporation. This excess depends mainly on the fuel composition and temperature and on its delivery rate.
Experimental tests have shown that said bubbles or foam give rise to excessive evaporation, with a vapor production which can be as much as 40% more than the volume of the delivered fuel.
In this respect, with the system adjusted in the stated manner this vapor excess cannot be drawn in by the delivery gun so that it escapes to atmosphere via the filler pipe, whereas if said vapor excess were recovered by suitably increasing the capacity of the positive displacement pump, there would be an inevitable vapor loss to atmosphere through the underground tank vent.